1. Field of the Invention
The present invention relates to a lithium secondary battery.
2. Description of the Related Art
Recently, a lithium secondary battery, which is rechargeable and lightweight and has high energy and output densities, has been widely used as an energy source for wireless mobile devices. Further, as alternative means to solve problems of air pollution and greenhouse gases caused from conventional internal combustion engine vehicles using fossil fuels such as a gasoline vehicle and a diesel vehicle, an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), or the like have been proposed. The lithium secondary battery has been researched as a power source for the alternative vehicles to the internal combustion engine vehicles.
The lithium secondary battery is classified into a lithium ion battery using a liquid electrolyte and a lithium polymer battery using a polymer electrolyte depending on a type of electrolyte, and is classified into cylindrical, prismatic, and a pouch shapes depending on a shape of an exterior material in which an electrode assembly is accommodated.
Among these, since the pouch type lithium secondary battery has an appearance that is made of a metal layer (foil) and a pouch film formed of multi-layers of a synthetic resin layer coated on upper and lower surfaces of the metal layer, the weight thereof may be more remarkably reduced than that of the cylindrical or prismatic lithium secondary battery using a metallic can, such that the pouch type lithium secondary battery may be lightweight and may be modified into various shapes.
However, in spite of the above-described advantages, since there is a limitation on a molding depth of the pouch film in a structural aspect thereof, cracks easily occur in the pouch film itself during a molding process for housing large sized battery cells, and the metallic layer is exposed from the cracked portion, which causes a reduction in life-span of the cells.
In addition, the lithium secondary battery is sealed by molding a case for housing the electrode assembly in a predetermined shape, and by sealing protruding portions of electrode taps. In this case, an unnecessary space is formed in the sealed portion, and thereby causes a reduction in capacity of the battery.
Korean Patent Laid-Open Publication No. 2007-0109080 discloses a pouch type lithium secondary battery having a rounded corner in which a bottom and a side of an electrode assembly housing part formed at a rear surface of a pouch are met, however, fails to solve the above-described problems.